(a) Field of the Invention
The present invention relates to a rotation information detector and more particularly, it relates to a rotation information detector for detecting rotation information such as the rotating speed and position of rotating bodies, using magnetoresistant elements.
(b) Prior Art
The magnetic encoder which is high sensitive, excellent in frequency characteristics, and simple in construction and which uses magnetoresistant elements to detect the rotating position and speed of a rotating body such as the drum and disc driven by the motor or the like has attracted attention as a rotation information detector.
The rotation information detector which uses the elements comprises forming slim elements on a substrate such the glass plate, arranging eight of them side by side and bridge-connecting every four of them. When the rotation information detector thus made is arranged adjacent to the rotating surface of the drum, for example, on which magnetic signals have been recorded, the magnetoresistant elements of the rotation information detector change their electric resistance responsive to change in magnetic field exerted by the rotating body and rotation information signals based on this change of their electric resistance can be picked up from the bridge circuit.
The magnetoresistant elements comprises forming a thin ferromagnetic film layer of permalloy, for example, on the substrate and then applying photoetching or the like to it to form plural slim pieces arranged side by side. In this case, however, etching solution gathers thick on both sides of the plural parallel-arranged magnetoresistant elements and those magnetoresistant elements which are located on these both sides are made more slim by the thick-gathered etching solution, as compared with the ones located nearer to the center.